Display apparatus with switched mode power supply to adjust frequency of control signal

Abstract

Disclosed is a display apparatus including: a display; a transformer configured to boost an input alternating current (AC) first voltage and output a second voltage; a switch configured to allow an electric current to flow or stop in the transformer based on a control signal; a power factor correction (PFC) converter configured to correct a power factor of the output second voltage, and output a direct current (DC) third voltage to the display; and a controller configured to modulate a frequency of the control signal so that the second voltage has a target level, and increase or decrease the frequency of the control signal within a specified range to synchronize with an AC period of the first voltage.

What is claimed is: 
     
       1. A display apparatus comprising:
 a display; 
 a transformer configured to boost an input alternating current (AC) first voltage and output a second voltage; 
 a switch configured to allow an electric current to flow or stop in the transformer based on a control signal; 
 a power factor correction (PFC) converter configured to correct a power factor of the output second voltage, and output a direct current (DC) third voltage to the display; and 
 a controller, comprising processing circuitry, configured to modulate a frequency of the control signal so that the second voltage has a target level, and increase or decrease the frequency of the control signal within a specified range to synchronize with an AC period of the first voltage, 
 wherein the controller is further configured to divide the AC period of the first voltage into a plurality of sections in specified units, and increase and/or decrease the frequency of the control signal for each of the divided sections. 
 
     
     
       2. The display apparatus according to  claim 1 , wherein the controller is configured to increase or decrease the frequency of the control signal based on phases for each of the divided sections. 
     
     
       3. The display apparatus according to  claim 1 , wherein the controller is configured to adjust a voltage of the control signal to correspond to the increase or decrease of the frequency. 
     
     
       4. The display apparatus according to  claim 3 , wherein the controller is configured to control the control signal, the voltage of which is adjusted, to have a constant average voltage during the AC period of the first voltage. 
     
     
       5. The display apparatus according to  claim 1 , wherein the controller is configured to identify a frequency of the first voltage, and identify a range, within which the frequency of the control signal is increased or decreased, based on the identified frequency of the first voltage. 
     
     
       6. The display apparatus according to  claim 1 , wherein the controller is configured to identify the AC period of the first voltage corresponding to a section from a point at which a highest voltage level of the first voltage is first identified to a point at which a highest voltage level is second identified. 
     
     
       7. The display apparatus according to  claim 6 , wherein the controller is configured to:
 detect a voltage level at specified time intervals for two periods of the first voltage, and identify a rising period and a falling period of the first voltage based on results of the detection; and 
 identify the highest voltage level based on a point, at which the rising period is switched over to the falling period. 
 
     
     
       8. The display apparatus according to  claim 7 , wherein the controller is configured to:
 calculate a first average level between a first detected level and a second detected level, and calculate a second average level between the second detected level and a third detected level, among the plurality of detected levels; and 
 identify a rising period and a falling period of the first voltage based on comparison between the first average level and the second average level. 
 
     
     
       9. The display apparatus according to  claim 7 , wherein the controller is configured to adjust the range, within which the frequency of the control signal is increased or decreased, based on the level of the first voltage less than a specified reference level. 
     
     
       10. The display apparatus according to  claim 1 , wherein the controller is configured to identify the frequency of the input AC first voltage, and identify a range, within which the frequency of the control signal is increased or decreased, based on the identified frequency. 
     
     
       11. The display apparatus according to  claim 1 , further comprising:
 a first rectifier configured to rectify a voltage received from an outside and output the AC first voltage; and 
 a second rectifier configured to rectify the second voltage boosted from the first voltage, 
 wherein the controller is configured to detect the rectified second voltage, and modulate the frequency of the control signal so that the second voltage has a target level, based on results of the detection. 
 
     
     
       12. The display apparatus according to  claim 1 , wherein the switch comprises first, second, third and fourth switching devices and,
 based on the first, second, third and fourth switching devices being selectively turned on or off, the switch is configured to correspond to one of a full bridge type or a half bridge type to receive a control signal, the frequency of which is increased or decreased within a specified range, from the controller. 
 
     
     
       13. The display apparatus according to  claim 12 , wherein the controller is configured to:
 turn on the second switching device and turn off the fourth switching device based on the input AC first voltage greater than or equal to a specified first reference voltage, and 
 output the control signal, the frequency of which is increased or decreased, to the first and third switching devices. 
 
     
     
       14. The display apparatus according to  claim 13 , wherein the controller is configured to output the control signal, the frequency of which is increased or decreased, to the first, second, third and/or fourth switching devices, based on the input AC first voltage being less than the specified first reference voltage.